Electro-Chemical Decomposition 55

211. Water, therefore; is in this respect merely one of a very
numerous class of substances,, instead of being the only one and
essential; and it is of that class one of the worst as to its
capability of facilitating conduction and sufTeing decomposition.
The reasons why it obtained for a time an exclusive character
which it so little deserved are evident, and consist, in the
general necessity of a fluid condition (i3o)r; in its being the
only one of this class of bodies existing in the fluid state at
common temperatures; its abundant supply as the great natural
solvent; and its constant use in that character in philosophical
investigations, because of its having a smaller interfering,
injurious or complicating action upon the bodies, either dis-
solved or evolved, than any other substance.

212. The analogy of the decomposing or experimental cell
to the other cells of the voltaic battery, renders it nearly certain
that any of those substances which are decomposable when
fluid, as described in my last paper (138), would, if they could
be introduced between the metallic plates of the pile, be equally
effectual with water, if not more so. Sir Humphry Davy found
that litharge and chlorate of potassa were thus effectual.1 I
have constructed various voltaic arrangements, and found the
above conclusion to hold good. When any of the following
substances in a fused state were interposed between copper
and platina, voltaic action more or less powerful was produced.
Nitre; chlorate of potassa; carbonate of potassa; sulphate of
soda; chloride of lead, of sodium, of bismuth, of calcium;
iodide of lead; oxide of bismuth; oxide of lead: the electric
current was in the same direction as if acids had acted upon
the metals. When any of the same substances, or phosphate
of soda, were made to act on platina and iron, still more power-
ful voltaic combinations of the same kind were produced.
When either nitrate of silver or chloride of silver was the fluid
substance interposed, there was voltaic action, but the electric
current was in the reverse direction.

Tf iii. Theory of Electro-chemical Decomposition

213. The extreme beauty and value of electro-chemical de-
compositions have given to that power which the voltaic pile
possesses of causing their occurrence an interest surpassing
that of any other of its properties; for the power is not only
intimately connected with the continuance, if not with the
1 Philosophical Transactions, 1826, p. 406.

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